Flexible hinge

ABSTRACT

A flexible hinge consisting of a single piece of rigid plastic material includes a thin flexible web portion between two inflexible end members, with flexible plastic material layers being bonded to opposing top and bottom faces of the web.

RELATED APPLICATION

This is a Divisional Application of application Ser. No. 09/321,943,Filed May 28, 1999, now U.S. Pat. No. 6,207,092 entitled “FLEXIBLEHINGE”.

FIELD OF THE INVENTION

The field of the present invention relates generally to flexible hinges,and more particularly to such hinges made of a polymer material.

BACKGROUND OF THE INVENTION

It known in the art to use polymer material or flexible plastic materialfor providing a flexible hinge or web connected between rigid andunflexible material. For example, in the power lawn mower industryindustrial safety standards have demanded that shields known as eitherdrag shields, safety shields or trail shields be connected across therear portion of the mower to prevent stones and other debris from beingthrown up at the operator as they walk behind power mower. As describedin greater detail below, one known type of trail shield includes a webof flexible Poly Vinyl Chloride (PVC) material connected between a rigidpivotal structure or tube like element of vinyl material, for connectionto the rear deck of a walk behind power mower, with the other end of theweb being secured to a relatively large diameter tubular structure orcurved end structure for gliding along and following the contours of alawn being mowed. Typically the PVC flexible web is laminated to thetubular attachment member, and the large diameter tubular curved groundfollower rigid vinyl structure. Because of the dissimilarity of thematerials, it has been found that a delamination problem exists duringuse. Due to the flexing back and forth of the web and the attached rigidmembers, the bonds therebetween tend to break away, ultimately causingpremature failure of the safety device, in this example, a drag shield.However, this problem can occur for any applications utilizing aflexible web of one material connected between rigid members of anothermaterial.

SUMMARY OF THE INVENTION

With the problems of the prior art in mind, the present inventionincludes two opposing and spaced apart rigid members of a first polymermaterial connected together by a centrally located web therebetween ofthe same material, with the web being a continuous structure emanatingfrom each one of the opposing rigid members, whereby the web is madethin enough to permitted it to be flexible. The rigid members includingthe web are in one embodiment of the invention fabricated from a commonrigid plastic material. A flexible plastic material is laminated to theinterconnecting rigid plastic web material on opposing sides thereof,for strengthening the web, and improving its impact resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are described below withreference to the drawings, in which like items are identified by thesame reference designations, wherein:

FIG. 1 shows a side elevational view of a trail shield of the prior art;

FIG. 2 shows a cross-sectional side elevational view of another form ofa drag shield of the prior art incorporating a flexible web of onematerial between two rigid members of another material;

FIG. 3 shows the flexing of a drag or trail shield as it is moved backand forth as attached to a walk behind power lawn mower;

FIG. 4 shows a cross-sectional view of one embodiment of the inventionapplied for use in a trail or drag shield;

FIG. 5 shows another embodiment of the invention for providing aflexible web between rigid members or structures having any given shape.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the flexible hinge of the present invention areprimarily described herein for use with walk-behind power lawn mowersafety shields, typically otherwise known as drag shields or trailshields. However, the use of a flexible hinge of the present inventionis not meant to be so limited. The flexible hinge of the presentinvention can be used for numerous applications suitable for plastictype flexible hinges, such as cabinet doors, tool box covers, storagechest covers, and so forth. However, by describing the present inventionin relation to walk-behind power lawn mowers drag shields, problems inthe prior art using such flexible hinges can be readily illustrated.

Drag or trail shields for walk-behind power lawn mowers are typicallyconstructed as shown in the side elevational view of FIG. 1. Typicaldimensions for such a drag shield are also shown in the figure. The dragshield globally denoted by reference 1 includes a rigid tubular element3 including a downward projecting elongated lip member 5 that isrectangular in shape as shown. The combination of the tubular portion 3and lip member 5 together form a pivotal structure 7 for attachment tothe rear deck of a walk-behind power lawn mower. The pivotal structure 7is typically mounted to the deck of the mower on a rod that is threadedthrough the hole 9 of the tubular portion 3, with the ends of the rod(not shown) securely mounted to opposing sides of the mower deck, as oneexample. As a result, the pivotal structure 7 is able to rotate aboutthe rod or other mounting means. A web 9 of flexible material, in thisexample includes opposing ends 11 and 13 each including an elongatedopen channel 12, 14, respectively. The end of the lip 5 of the pivotalstructure 7 is mounted within the channel 12 in the upper end 11 of web9, shown through use of known bonding methods. The channel 14 in thelower end 13 of web 9 has the end of a lip 15 protruding from a ballstructure 17, in this example, bonded thereto. The ball structure 17includes either an elongated structure 19 having a circular crosssection, or some other form of a curved elongated element for followingor dragging along the ground and moving over various contours of theground as a walk-behind power mower is moved back and forth in cutting alawn, as will be described in greater detail below. Typically thepivotal structure 7 and slide ball structure 17 consists of an extrudedor molded rigid vinyl material, and the web 9 of flexible PVC (PolyVinyl Chloride).

In FIG. 2, an alternative known design for a drag shield is shown in aside elevational view. The pivotal structure 21 includes an upperelongated tubular member 23 and a downwardly projected lip 25 thatincludes an interior rectangular portion, and terminates into a taperedand substantially pointed free end 27, as shown. The lower-most slideball structure, instead of having a lip 15 projecting rectangularly aswith the slide ball 17 of the example of FIG. 1, includes a tangentiallyprojecting lip portion 29 that terminates in a tapered pointed end 31,as shown. As a result, the flexible web 33 includes an elongatedV-channel 35 at its upper end, and a similar elongated V-channel 37 atits lower end, for receiving and bonding to the end lip portions 27, 31,respectively, as shown. As in the previous example, the pivotalstructure 21 and slide ball 28 consist of extruded or molded rigid PVC,whereas the flexible web 33 consists of molded or extruded flexible PVC.

For the two examples of the drag shield shown in FIGS. 1 and 2, thedissimilar plastic materials of the web 9 relative to the pivotalstructure 7 and slide ball of 17 of FIG. 1, and similar correspondingelements of FIG. 2, are laminated together, typically during extrusion,to form a secure bond therebetween. However, there is always apossibility that the bonds between the dissimilar plastic materials maydelaminate, causing failure of the drag shield and a potential safetyhazard. The power mower industry has attempted to overcome this problemthrough use of quality control testing procedures for insuring that froma statistical basis drag shields meet “Government and Long Lawn CareProducts Manufacturers Standards”. However, this statistical testingused does not permit every drag shield produced to be tested. Thispresents a potential safety hazard in that plastic hinges, as used inknown drag shields, undergo extreme bending and flexing during use of anassociated walk-behind power mower. As shown in FIG. 3, as a drag shield1 is moved over a ground surface 39 during forward motion of anassociated mower in the direction of the arrow shown, the web 9, 33 tendto bend as shown, and in the reverse motion of the power mower wouldtend to bend in the opposite matter, as shown. Accordingly, extremestress is placed upon the bonded portions of the drag shields 1 duringuse. If the resulting stress applied to the bonded joints of dissimilarplastic material, causes the bonds to break, for example, the dragshield may fail due to the web portion tearing away from the pivotalstructure.

To overcome the problems in the prior art, the present inventorrecognized that the stress placed upon bonded joints between dissimilarplastic materials must be overcome or substantially reduced, to enhancethe reliability of such products using flexible hinges as drag shields.After much experimentation in a long-term development project, a newflexible hinge was developed that substantially overcomes the problemsof delamination and/or bond breakage in the prior art. With reference toFIG. 4, as configured for use in an improved drag shield 41, oneembodiment of the invention includes in a web portion 43 having a threelayer configuration of laminated materials. The centermost web layer 45consists of the same material as the upper pivotal structure member 47,and lower slide ball member 49, all of which in the preferred embodimentare extruded or molded together in a single piece. The pivotal structure47 includes an elongated tubular member 51, with a regularly directedand downwardly projecting substantially rectangular limp portion 53,having downwardly projecting converging end portions 55 and 57terminating with the relatively thin extension thereof forming the webportion 45. Similarly, the slide ball structure 49 includes an elongatedportion 59 having a circular cross section, with a radially directed andupper wardly projecting lip portion 53 that is substantially rectangularin cross section, with its uppermost portion having ends 63, 65converging to the lowermost portion of the central web 45. In thepreferred embodiment of the invention, the pivotal structure 47, andslide ball structure 49 consists of a rigid Olefin material, such asMontell 7823 (trademark of Montell, Inc.) or equivalent. This materialis a high impact copolymer polypropylene made utilizing metallocenecatalyst technology, that compared to other materials has superiormechanical and thermal properties. Although this plastic material is arigid material, the present inventor determined that by making thethickness of the web 45 of this material about 0.02 inch, the web couldbe made to be flexible in this area.

To strengthen and reinforce the web area, a layer of flexible Olefinmaterial is formed in a first layer 67 on one side of the central web45, and a similar layer 69 on the opposite side of the material of thecentral web 45. In the preferred embodiment, the flexible Olefin isprovide by either Dow/Dupont 8480 (manufactured by a Dow CorningCompany, and Dupont Corporation) or Exxon Exact 0201 (manufactured byExxon Corporation), or the equivalent. This material is a metallocenepolyethylene, more particularly a saturated ethylene octane copolymer.Compared to other plastic materials, this material provides superiorlong term stability, improved weatherability, and high impactresistance.

Also in a preferred embodiment, the outer flexible plastic webbed layers67 and 69 are laminated directly to the rigid plastic material of thecentral web 45 in an extrusion process. Further in the preferredembodiment, the thickness each one of the outer layers 67 and 69 isabout 0.030 inch, making the total thickness of the central web to beabout 0.08 inch, in this example. The flexible plastic layers 67 and 69serve not only to strengthen the central web layer 45 against breakageor cracking, but also insure that the inventive drag shield meetsvarious impact test requirements, such as CPSC No.1205.4, ANSI\OPEI B71.1, and EN 836, and other specifications introduced by variousmanufacturers for guaranteeing the safety performance of drag shields.Tests completed of the inventive design in FIG. 4 have proved that thedelamination problem of the prior art has been substantially eliminated,due in large part to the avoidance of any discontinuities or breaks inthe material, such as by joints, between the centralmost web portion 45,and the rigid end structures, in this example being the pivotalstructure 47 and slide ball structure 49, respectively. However,although the Olefin materials indicated previously are at the presenttime considered the preferred materials for use with the flexible hingestructure of the present invention, such materials are not meant to belimiting. It is believed that improvements can be made to the inventiveflexible web through the careful selection of the thicknesses of thecentral web portion 45, and outer web portion layer 67 and 69, inaddition to modifying the plastic materials used for these portions forimproving impact resistance and flexibility for meeting differentrequirements and uses for the inventive flexible web.

As has been indicated previously, the flexible web of the presentinvention is not limited to use with walk-behind power lawn mower dragshields or trail shields, but has multiple uses in any applicationswhere a plastic hinge is used. For example, as shown in FIG. 5, ageneralized application of the inventive flexible hinge 80 is shownconnected between two rigid plastic end members 82 and 84. As with theapplication for use in the drag shield, the inventive flexible hinge 80includes a thin central web layer 86 consisting of the same rigidplastic materials as end portions 82 and 84, and being formed as asingle piece therewith thereby avoiding any discontinuities or breakstherebetween. Flexible plastic layers 88 and 90 are bonded on opposingsides of the rigid plastic central web portion 86. The central rigidplastic material of web portion 86 is made thin enough to be flexible.

In static pull tests using 100 pounds static weight over 50% of theprofile the present inventive flexible hinges using the identifiedpreferred Olefin materials in the drag shields had no breaks orseparation of the web from the rigid members. In comparison, dragshields of rigid PVC and flexible PVC failed at over 50 pounds staticweight over 50% of their profile.

Although, various embodiments of the invention have been shown anddescribed, they are not meant to be limiting. Those of skill in the artmay recognize certain modifications to these embodiments, whichmodifications are meant to be covered by the appended claims.

What is claimed is:
 1. A flexible hinge comprising: an inflexible first rigid end member; an inflexible second rigid end member; a thin flexible first web layer connected between, and consisting of the same rigid plastic material as, said first and second rigid end members; a flexible second web layer bonded to one side of said first web layer; and a flexible third web layer bonded to another side of said first web layer opposing its one side, wherein said flexible second and third web layers consist of a different material than that of said first web layer.
 2. The flexible plastice hinge of claim 1, wherein said flexible plastic material is a flexible Olefin material.
 3. The flexible plastic hinge of claim 1, wherein said first and second rigid end members, and first web layer consist of a rigid Olegin material.
 4. The flexible plastic hinge of claim 1, wherein said first and second rigid end members, and said flexible first web layer, consist of rigid Olefin material, and said second and third web layers consist of a flexible Olefin material.
 5. The flexible plastic hinge of claim 1, wherein said rigid plastic material is a rigid Olefin material.
 6. The flexible plastic hinge of claim 3, wherein said rigid Olefin material consists of a high impact copolymer polypropylene material derived from metallocene catalyst technology.
 7. The flexible plastic hinge of claim 4, wherein said rigid Olefin material consists of a high impact copolymer polypropylene material derived from metallocene catalyst technology, and said flexible Olefin consist of metallocene polythylene.
 8. The flexible plastic hinge of claim 5, wherein said rigid Olefin material is a high impact copolymer polypropylene material derived from metallocene catalyst technology.
 9. The flexible plastic hinge of claim 2, wherein the flexible Olefin material is a metallocene polythylene material.
 10. A flexible hinge comprising: an inflexible first rigid end member; an inflexible second rigid end member; a thin flexible first web layer connected between the first and second end rigid members, and said thin flexible first web layer and said first and second rigid end members consisting of the same rigid piece of high impact copolymer polypropylene material derived from metallocene technology; a flexible second web layer bonded to one side of said first web layer; and a flexible third web layer bonded to another side of said first web layer opposing its one side, wherein said flexible second and third web layers consist of a different material than that of said first web layer, wherein each of said second and third web layers consist of metallocene polyethylene material, said combination of materials for said first through third web layers substantially preventing delamination of these layers and breakage or cracking of said first layer. 